The present invention relates to a rotary machine having therein a rotating detection mechanism for detecting rotational speeds or the number of revolutions as a frequency signal.
Nowadays, in order to reduce the thickness of electrical machinery and apparatus having therein a rotary machine, for example, a cassette tape recorder which is convenient for portable use, as shown in FIG. 1, provision is made of a flat coreless motor 1 as a rotary machine for running a magnetic tape with a constant speed, and the coreless motor 1 is arranged by the side of a cassette chamber for receiving a tape cassette 2. The thickness of the cassette tape recorder depends on the thickness of the flat coreless motor 1.
In order to run the magnetic tape with a constant speed, the flat coreless motor comprises a servo circuit, by which the difference between the previously set reference rotational speed and the actual rotational speed is measured or detected, and the rotational speed is automatically adjusted until the detected difference becomes zero.
There has been provided, as such a motor, a rotary machine in which a frequency generator for generating a frequency output signal corresponding to the rotational speeds is built in the motor body. This rotary machine is so constructed that a disk shaped armature magnet is tightly fitted onto a rotor shaft of the motor, and a coil unit is loosely mounted around the armature magnet.
In such a construction, however, the frequency generator is incorporated in the motor body so that the thickness of the coreless motor is increased by the part occupied with the frequency generator and can not be made equal to the thickness of the tape cassette. Therefore, it is impossible to make the cassette tape recorder thin.